This invention relates to a balancing machine for compensating imbalance factors in rotating bodies having a surface of rotation about an axis, said factors being compensated by applying one or more balancing masses. Typically the machine of the invention is provided for balancing motor vehicle wheels, in which the balancing masses are applied to the wheel rim; however it can also be applied to other rotating bodies, such as flywheels.
Balancing machines, in particular for motor vehicle wheels, have been known for some time possessing a support and rotation shaft (i.e. a main shaft) on which the wheel is fixed with its axis of rotation coaxial to the axis of the shaft, which rotates the wheel.
On these machines, first sensor means having for example a movable sensor arm firstly determine the axial position of at least one transverse balancing plane (usually two planes), i.e. a plane perpendicular to the axis of rotation, passing through the region chosen by the operator on which to apply a respective balancing mass, said choice deriving from considerations of various kinds, for example to make the balancing mass invisible from the outside, or because the surface of the body in that plane is particularly suitable for application of the balancing mass. In addition to the axial position of the plane, the radial coordinate of the wheel rim surface in correspondence with said balancing plane is also determined. At the same time, using second sensor means comprising for example an encoder able to monitor the angular position of the main shaft, every angular position of the body relative to a reference position can be determined.
The main shaft of the machine is then rotated, and the imbalance factors are determined by long known methods using suitable sensing means. The data originating from the first and second sensor means and the data relative to the imbalance are then processed by a processor means, and the value of the balancing masses and the position of their point of application to the wheel rim in the chosen balancing plane are then determined.
The balancing masses, of the calculated value, are then applied in the calculated positions. This operation is carried out in various ways depending on the type of weights used and the balancing program. Given the increasing use of aluminium alloy wheel rims, there is an increased need to apply balancing masses by adhesive to the inside of the body rim. To ensure maximum balancing precision, the balancing mass must be positioned with extreme accuracy in the respective balancing plane and in the calculated angular position therein.
For this purpose various systems have been developed which provide for assisted application of the balancing masses.
The most improved of these systems, illustrated in U.S. Pat. No. 6,244,108, comprises the use of an oscillating indicator means connected to the processor means to project a light point onto the application surface of the wheel rim in the position of application of the balancing mass calculated by the processor. This indicator means determines the position of the application point with the aid of means which halt the shaft rotation in the calculated angular position.
This system facilitates the application of the balancing masses and makes it more precise.
However the automatic search for the point of application of the balancing mass requires complex and costly means for controlling the oscillation of the light-emitting indicator means and rigorous control of the action of the brake and motor to halt the shaft in the exact angular position, so increasing the machine cost and complexity.
An object of the invention is to improve the machines of the initially described type, in particular of the aforesaid type, such as to eliminate the described defects.
This and further objects are attained by the invention as characterised in the claims.
The invention is based on the fact of comprising a means arranged to acquire images from that surface of the body on which the balancing masses are to be applied (i.e. the inner surface of the wheel rim including its end edges, in the case of a motor vehicle wheel) and a display means connected to the processor means (arranged to calculate the value of the balancing mass and the position of its point of application on the application surface of the body in correspondence with the balancing plane), which displays said images on a screen accessible to the operator, the processor means indicating on the screen the position of the point of application of the balancing mass in relation to those images originating from the application surface which appear on it. Specifically, to indicate the point of application of the balancing mass, the processor means displays an optical pointer which appears on the screen at said point of application, superposed on the acquired image of the application surface (inner surface of the wheel rim).
Preferably, to automatically halt the rotation of the wheel support and rotation means, a means is provided connected to the second sensor means and arranged to halt the wheel in an angular position such that the point of application of the balancing mass falls within any region of the field visible on the screen.
In use, in accordance with the known art, first measurement sensor means firstly determine the axial position of at least one transverse balancing plane in which the operator chooses to apply a respective balancing mass, and the radial position of points on the application surface of the body corresponding with said balancing plane, while by second sensor means the machine monitors the angular position of the wheel; the wheel is rotated and by suitable means the machine determines the imbalance factors thereon, these being processed by a processor means together with the data originating from the first and second sensor means, the value of each balancing mass and the position of its point of application on the application surface (inner surface of the wheel rim) being determined. According to the invention, images originating from the body are acquired by the image acquisition means, said images being displayed on the screen accessible to the operator; to apply the balancing masses the body is brought into an angular position such that the point of application of the masses falls within any region of the field visible on the screen, on the screen there being indicated the position of application of the balancing mass in relation to the image which appears on it.
By virtue of the invention, the weight application is quick and precise, and in addition the complex and costly control system for the light point provided in the prior art is eliminated.
Precise control during the braking of the body is not required because the optical position pointer moves over the screen on the basis of the angular position in which the body is halted.
Finally, the invention can also be used for applying spring weights to the edge of the body.